Distortion correcting impulse repeater



June 17, 1947. H. J. M cREARY 2,422,309

DISTORTION CORRECTING IMPULSE REPEATER Filed March 10, 1945 INVENTOR.HAROLD J. M CREARY ATTORNEY- Patented June 17, 1947 UNITED STATES PATENTOFFICE 2,422,30

DISTORTIONYCORRECTING IMPULSE REPEATER Harold J. McCrear-y, Lombard,Ill, assignor to Automatic Electric Laboratories, 1110., Chicago,

111., a corporation of Delaware Application March 10, 1945, Serial No.581,984

9 Claims.

The present invention relates to impulse repeaters for use in signalingsystems such as auto- When impulses are transmitted over long lines suchas are sometimes encountered in telephone limits for reliable operationof the selecting apparatus.

The principal object of the present invention is to provide an improvedvention and adapted to be controlled by impulses transmitted over aconventional telephone line;

. igure 2 is a schematic diagram of a modification of Figure 1 in whichan Eccles-Jordan trigger circuit is substituted for the pair of gasdischarge tubes employed in Figure 1.

Briefly described, the invention consists in utithe secondary winding,nected in series across the secondary winding in series with twocondensers. A pair of gaseous discharge tubes have their cathodesconnected to the junction between the two resistors and each has acontrol electrode with an impedance that is common to the pair ofAcondenser is connected directly between the anodes of the tubes so asto cause either tube to be deionized when the alternate tube fires.

is also connected in The invention will now be described in detail withreference to the accompanying drawing. Referring to Fig. 1, there isshown a subscriber substation set having an impulsing device andconnected over line 2 to a source of potential in series with relay 3.Condenser 4 and resistor 5 are serially connected in multiple withthelower winding of relay 3. The lower portion of resistor 5 isconnected between the grid and cathode of vacuum tube 5. The anodecircuit of tube 6 is coupled by means of transformer (to the controlgrids of the gaseous discharge tubes 8 and 9. An impulse repeatingrelayl0-is connected in series with the anode circuit of tube Hl.Contacts H may be used to repeat impulses corresponding to thoseproduced by the impulsing device I to switching apparatus such as wouldnormally be controlled-by the line relay 3.-

The line 2 has been represented as an H network of resistance elements.Actually the series resistance of the line is uniformly distributed, butthe shunt resistance may be either distributed or lumped as itmay beproduced by a fault at one or more points-in the line or may beunavoidable distributed leakage resistanc The line-willalso havedistributed capacity. The substation set includes the usual telephoneringer 12 which is connected across line 2 in series with condenser 13.Although only one substation sethas been shown it should be understoodthat as many as twenty sets may be similarly connected across the line.They may be distributed alon the line or a number may be connected atthe same point.

Typical values for such a telephone line are 0 to 1200 ohms seriesresistance-and 5000 ohms to infinite shunt resistance. The ringers, suchas 12, may each have a resistance of 1600 ohms and the condensers, suchas l3, may each have a capacitance of one niicrofarad. The relay 3usually has a resistance of 200 ohms per winding and the battery voltageusually has a nominal value of 48 volts. Due to the charginganddisharging of the ringer condensers during impulsing the currentflowing through relay 3 is greatly distorted. The. actual wave shapedepends upon the line constants and the number and distribution of theringers. oftentimes oscillations in the line current occur each timethat the contacts of the impulsing device open. At the instant thesecontacts open the ringer condensers commence to charge in series withthe ringers, the series resistance of the line, the windings of relay 3,and the battery. The flux in the core of relay 3 com mences to collapsecausing a voltage to be induced in the windings of relay 3 which tendsto maintain the current flowing in the line. As a result of this selfinduced voltage in relay 3 the potential across line 2 at the relay maybecome higher than the battery voltage. When this occurs the ringercondenser continues ,to charge until it reaches a potential equal tothatacross the line at relay 3 at which time the condenser commences todischarge causing a reversal in line current to take, place and causinga flux in the opposite direction to normal to be built up in the core ofrelay 3. The ringer condenser continues to discharge until it againreaches a potential equal to that across line 2 at relay 3, whichpotential will at this time be less than the battery potential. The linecurrent then again reverses and the same cycle of events is repeated butwith reduced amplitude. Ordinarily, the amount of damping present insuch an impulsing circuit is high enough to so reduce the amplitude ofthe first reversal of line current as to prevent reoperation of theimpulse responding relay. However, the present impulse repeater isintended to be responsive to the rate of change in the line currentrather than the magnitude of the current and it therefore becomesnecessary to eliminate such oscillations. This is accomplished by meansof rectifiers l4 and 15, each of which is-connected across one of thewindings of relay 3 so as to be normally non-conductive. Now when thecontacts of the impulsing device i open, the two windings of relay 3 arein effect short-circuitecl, thus preventing the potential across theline? at relay 3from exceeding the battery due to the collapse offlux'in the core of relay 3. As the ringer condenser is prevented fromcharging to a potential higher than the battery voltage no reversal inline current takes place. The short-circuiting of relay-3 renders itslow-to-release and may prevent it from responding to the impulsescompletely. Since the function of the impulsing contacts normallycontrolled by relay 3 are now taken over I! the slow release action ofrelay 3 is no disadvantage and in fact it will be advantageous incaseswhen a slow to release relay, such as the holding relay employed intelephone systems, must be held operated by contacts of relay 3 duringimpulsing. Due to the above described action of the rectifiers the linecurrent always decays exponentially when the impulsing contacts open.The line current also rises exponentially when the impulsing contactsclose. If all of the line current flowed through relay 3 the voltageacross relay A would be a maximum at the instant the impulsing contactsopened and would decay exponentially. This voltage would also beopposite in polarity to the normal voltage across the relay. Since therectifiers prevent such a reversal of polarity of the voltage acrossrelay A, the'voltage will actually drop to substantially Zero at theinstant the impulsing contacts open and may later rise slowly accordingto an exponential law to the steady state open circuit value which isdetermined by the value of the line shunt resistance. When the impulsingcontacts close, the voltage across each of the windings of relay A willinstantly rise to onehalf of the battery voltage and will decayexponentiallyto the steady state closed circuit value which isdetermined by the line resistance. It is thus apparent that rapidchanges in the potential across either winding of relay 3 take place atthe instants of make and break of the impulsing contacts. These changesin potential across the lower winding of relay 3 also appear acrossresistor 5. The condenser 4 serves as a blocking condenser to preventthe steady voltage drop whichnormally appears across relay '3 fromaffecting the amplifying tube 5. The cathode of tube 6 is connected tothe negative terminal of the battery through resistor IT to provide theproper bias for operation of the tube as a linear amplifier. Thecathoderesistor i1 .is bypassed by condenser [8 to prevent degenerationof the steep wave fronts which must be amplified by the tube. A portionof the signal voltage developed across resistor 5 by operation of theimpulsing device I is applied to the grid of tube '6 through resistorI9. The purpose of resistor I9 is to prevent excessive grid current fromflowing in case the adjustable tap on resistor 5 is set high enough tocause the grid to at times be driven positive. The screen grid of tube 6is connected to an adjustable tap on resistor 20 which is bridged acrossthe battery. The screen grid is also bypassed to the cathode bycondenser 2I. The anode of tube 6 is connected to the positive terminalof the battery, which is usually grounded, through resistor 22. Theprimary winding of transformer I is connected across resistor 22 inseries with condenser 23. Due to the high plate resistance of pentodetype tubes the plate current of tube 6 will have substantially the samewave shape as the signal voltage. The voltage induced in the secondarwinding of transformer I will be proportional to the rate of change ofcurrent in the primary and thus will consist of sharply peaked impulseswhich occur at the instants of make and break of the impulsing contacts.The polarity of these impulses Will also be opposite for makes andbreaks of the impulsing circuit. The secondary of transformer 1 isconnected to resistors 24 and 25 in series through condensers 26 and 21.The values of these condensers and resistors are chosen so as to providea Very low time constant whereby the magnitude of the displacementcurrent flowing through them in response to a peaked voltage impulse inthe secondary of transformer I will be large but the displacementcurrent which flows due to other signals, such as voice currents, willbe small. The junction point between resistors 24 and 25 is connected tothe negative battery terminal and the other ends of resistors 24 and 2-5are connected to the control electrodes of tubes 8 and 9, respectively,through resistors 28 and 29. The cathodes of tubes 8 and 9 are connectedto an adjustable tap on resistor 30 which is bridged across the battery.The voltage drop across the top section of resistor 30 thus biases thecontrol electrodes of tubes 8 and 9 negatively with respect to thecathodes. This section of resistor 30 is bypassed by condenser 35. Theanode of tube 8 is connected through resistor 3| and impedance 32 toground or positive battery. The anode of tube 9 is connected throughrelay I 0, resistor 33 and impedance 32 to ground or positive battery.Impedance 32' may conveniently take the form of a relay similar to relayI0 but without springs. One of the tubes 8 or 9, which are of thegaseous discharge type, is always ionized. In the drawing it is assumedthat tube 9 is the one that is ionized when the impulslng circuit isclosed.

When the impulsing circuit is opened the resulting displacement currentflowing in resistors 24 and 25 tends to make the control electrode oftube 8 positive and the control electrode of tube 9 more negative.Consequently tube 8 becomes ionized. During the time that tube 8 wasdeionized condenser 34 became charged to a potential equal to thevoltage drop produced across relay I0 andresistor 33 by the anodecurrent of tube 9. 'When tube 8 becomes ionized it produces a voltagedrop in resistor 3I which lower the anode potential of tube 9momentarily since the potential across condenser 34 cannot changeinstantaneously. Tube 9 thus becomes deionized and condenser 34discharges and recharges in the reverse direction to a potential equalto the voltage drop produced in resistor 3| .by the anode current oftube 8. The impedance element 32 assists in lowering the anode potentialof tube 8 when tube 9 fires since it is common to the two tubes. Thecircuit is operative without impedance 32 but more reliable operation isobtained when it is used.

When the impulsing circuit is closed the resulting displacement currentflowing in resistors 24 and 25 tends to make the control electrode oftube 9 positive and the control electrode of tube 8 more negative.Consequently tube 9 becomes ionized and brings about the deionization oftube 8 in a similar manner to that previously described for theionization of tube 8 and the deionization of tube 9.

It is now apparent that tube 9 will be conductive during the time thatthe contacts of the impulsing device I are closed and that tube 9 willbe non-conductive during the time that the contacts of the impulsingdevice I are open. Since the repeater is controlled by the rate ofchange of line current rather than the magnitude of the current the onand off conduction periods will be substantially the same as the breakand make periods of the impulsing contacts regardless of the distortionintroduced by the line or impedances bridged across the line. The anodecurrent of tube 9 may be used to control a stepping switch or otherselective switching apparatus directly or may control a relay asillustrated. Since the anode current of tube 9 is a square wave therelay III will accurately reproduce impulses, corresponding to the makeand break periods of the impulsing device I, at its contacts I I.

In an actual test it was found that no perceptible variation in theimpulse ratio of the contacts II could be observed on an impulse ratiometer when the characteristics of the line 2 and the number of ringers,such as I2, were variedover the maximum range encountered in telephonepractice. In this test the following circuit values were employed.

Tube 6 6A0? Tubes 8 and 9 2050 Condenser I8 10 mf. Condenser 2| 10 mi.Condenser 23 1 mf. Condensers 26 and 21' .04 Inf. Condenser 35 10 mi.Condenser 34 5 mi. Transformer 7 2 to 1 step up turns ratio. Relay I0 30ohms Impedance 32 200 ohms Resistor 5 50,000 ohms Resistor I9 100,000ohms Resistors I1, 3|, and 33 300 ohms Resistor 20 1,000 ohms Resistors22, 24, 25, 28, and 29 10,000 ohms Resistor 30 500 ohms Referring now toFig. 2, there is shown a conventional Eocles-Jordan trigger circuitwhich is adapted to control relay I0 in accordance with the impulsesinduced in the secondary winding of transformer 1 by the anode currentof tube 6 in a similar manner as described for the gaseous dischargetubes 8 and 9 of Fig. 1. Each of the tubes 36 and 31, which are of thehigh vacuum type, has a separate plate load impedance. The plate loadimpedance for tube 31 being relay I0 and that for tube 36 being asimilar impedance 38 which may be a relay similar to relay I0 butwithout springs. The plates of each of the tubes are coupled to thegrids of the alternate tube through resistors 39 and 40 which arebypassed by small condensers H and 42, respectively. The connectionsbetween the plates and grids of the tubes tend to make each of the gridspositive with respect to the cathodes. This positive bias on the grids,equal to the voltage drops in resistors 24 and 25, is opposed by thevoltage drop in the upper section of resistor 30. The plate currents oftubes 36 and 31 cannot remain equal because the circuit is unstable. Anyslight increase in the grid potential of one of the tubes will cause anincrease in its plate current. The voltage drop in its plate loadincreases and thus reduces the potential on the grid of the other tube.The plate current of the other tube then decreases causing a decrease inthe voltage drop in its plate load thus further increasing the gridvoltage of the first tube. This action continues until the plate currentof the first tube reaches a maximum value and the plate current of theother tube is cutoiT. The action is accelerated by the condensers 4| and42 because they increase the instantaneous change in voltage impressedon the grid of one tube by a change in plate current of the other tube.f the circuit constants are properly chosen the grid potential on thenon-conducting tube can be made greater than the cut-off value so thatminute changes in its grid voltage will not result in any flow of platecurrent and thus operation as a multivibrator is prevented. However, anincrease in the grid potential which is sufficient to produce a flow ofplate current in the tube formerly cut off will resuit in the cumulativeaction described above which continues until the tube which was formerlyconductive is cut off. For the purpose of the present invention, thetransfer may be considered as occurring instantaneously. Assuming thattube 3: is conducting, which is the normal condition when the impulsingcircuit is closed, the voltage impulse induced in the secondary oftransformer I by the change in plate current of tube 6 in response tothe contacts causes the grid voltage of tube 35 to increase and that oftube 31 to decrease. Tube 3 thereupon becomes conductive and tube 31becomes cut-oiT. This condition will be sustained until a furtherimpulse of reversed polarity is induced in the secondary of transformerl in response to the closing of the impulsing contacts. The platecurrent of tube 31', being substantially a square wave, causes relay H)to accurately repeat impulses corresponding to the make and breakperiods of the impulsing device I. It should be noted that the values ofresistors 40 and 24 are so high as to draw an inappreciable currentthrough relay l and thus do not interfere with the release of the relay.Suitable values. for the circuit components of Fig. 2 are indicatedbelow.

Tubes 36 and 3? 6N7 Condensers 26 and 21 .002 mi. Condensers 4i and 4250 mmf. Resistors 24, 25, 30, and ii 250,000 ohms Resistor 38 1,000 ohmsRelay l0 30,000 ohms Impedance 38 30,000 Ohms Although the invention hasbeen illustrated in its most simplified form, it should be obvious thatnumerous modifications are possible. For example, instead of the impulserepeater being associated with a single line, it may be made available:

opening of the impulsing 8 to any one of a number differentcharacteristics. In this case the independence of the repeated impulsesfrom the line characteristics becomes an extremely desirable attributeof the repeater. Although only a single subscriber substation setconnected at the end of the line has been illustrated, it should beapparent that several such sets located at different points along theline may be used. Of course it is understood that only one set may beused at a time, the impulse transmitter of each set being disconnectedwhen not in use by the usual hookswitch. The ringers of each of the setswill always be connected to the line. The distortion in the line currentwill be different for each location of the impulsing device, but theoperation of relay III will be unaffected by such variations.

What is claimed is:

1. In a signaling system, an impulsing circuit including an interruptingdevice, a line, an impedance, and a source of potential, a pair ofgaseous discharge tubes each having an anode, a cathode, and a controlelectrode, means responsive to a decrease in the voltage across theimpedance for initiating a discharge between the cathode and controlelectrode of one of said tubes and responsive to an increase in thevoltage across the impedance for initiating a discharge between thecontrol electrode and cathode of the other of said tubes whereby onetube is fired at the instant that the interrupting device opens saidimpulsing circuit and the other tube is fired at the instant that theinterrupting device closes said impulsing circuit, and means in theanode circuits of said tubes for extinguishing either tube in responseto the firing of the alternate tube.

2. A signaling system as claimed in claim 1 in which said first meanscomprises a amplifier hav ing input and output circuits, the inputcircuit or said amplifier being coupled to the impedance and the outputcircuit of said amplifier being coupled to the contol electrodes of saidgaseous discharge tubes in push-pull relationship.

3. In an impulse repeater; a circuit over which impulses are at timestransmitted; a pair of gaseous discharge tubes each having an anode, acathode, and a control electrode; means coupling the control electrodesof said tubes to said circuit so as to initiate a discharge in one tubeat the beginning of an impulse transmitted thereover and to initiate adischarge in the other tube at the end of the impulse; a circuit betweenthe anode and cathode of one of said tubes including a resistor, animpedance, and a source of direct current; a circuit between the anodeand cathodeofr" the other of said tubes including a second resistor,said impedance, and said source of direct current; a condenser connectedbetween the anodes of said tubes; said condenser, impedance, andresistors cooperating to extinguish either tube in response to theionization of the alternate tube and an impulse repeating relay having awinding connected in series with the anode circuit of one of said tubes.

4. In an impulse repeater, a transformer having two windings, means forcausing a periodic current representing impulses to flow through one ofsaid windings, a series circuit comprising a condenser and a pair ofresistors connected across the other of said windings, the inducedvoltage in said other winding being substantially proportional to therate of change in current in said one winding and the current flowing insaid series circuit varying in accordance with the rate of change insaid induced voltage, a pair of therof lines each having mionic tubeseach having an anode, a cathode, and a control electrode, a connectionbetween the cathodes of said tubes and a junction between saidresistors, connections between the control electrodes of each said tubesand opposite ones of said resistors, said connections causing one ofsaid tubes to become conductive in response to an increase in the rateof change in current in said one Winding and causing the other of saidtubes to become conductive in response to a decrease in the rate ofchange in current in said one winding, means interconnecting said tubesfor rendering a conductive one of said tubes non-conductive in responseto the other tube becoming conductive, and an impulse repeating relaycontrolled by the anode current of one of said tubes.

5. In an automatic telephone system, a subscriber substation setincluding an impulse transmitter, a relay, a source of potential forsupplying transmission battery to said substation set, a line connectingsaid substation set to said source of potential in series with saidrelay, asymmetrical conductance means shunting said relay forsuppressing oscillations otherwise produced in said line in response tothe operation of the impulse transmitter, a second relay, and thermionictube means controlled by the transient voltages produced across saidfirst relay in response to the operation of the impulse transmitter foroperating said second relay in accordance with the impulses transmitted.

6. In a signaling system, an impulsing circuit including an interruptingdevice, a line, and a source of potential, a pair of thermionic tubeseach having an anode, a cathode, and a control electrode, means coupling1e control electrodes and cathodes of said tubes to said line inpushpull relationship whereby one of said tubes is rendered conductiveat the instant that the interrupting device opens said impulsing circuitand the other of said tubes is rendered conductive at the instant thatthe interrupting device closes said impulsing circuit, meansinterconnecting said tubes for renderin either one of the tubesnon-conductive in response to the other tube becoming conductive, and animpulse repeating relay controlled by the anode current of one of saidtubes.

7. In an automatic telephone system, a subscriber substation setincluding an impulse transmitter, an inductance coil, a source ofpotential for supplying transmission battery to said substation set, aline connecting said substation set to said source of potential inseries with said response to the operation of the impulse transmitter, arelay, and

trolled by the transient voltages produced across said inductance coilin response to the operation of the impulse transmitter for operatingsaid relay in accordance with the impulses transmitted.

8. In an automatic telephone system, a subscriber substation setincluding an impulse transmitter, an inductance coil, a source ofpotential for supplying transmission battery to said substation set, aline connecting said substation set to said source of potential inseries with said inductance coil, a pair of thermionic tubes each havingan anode, a cathode, and a control electrode, means coupling the controlelectrodes and cathodes of said tubes to said inductance coil inpush-pull relationship whereby one of said tubes is rendered conductiveat the instant that the impulse transmiter opens said line and the otherof said tubes is rendered conductive at the instant that the impulsetransmitter closes said line, means interconnecting said tubes forrendering either one of the tubes non-conductive in response to theother tube becoming conductive, and an impulse repeating relaycontrolled by the anode current of one of said tubes.

9. In an automatic telephone system, a subscriber substation setincluding an impulse transmitter, an inductance coil, a source ofpotential for supplying transmission battery to said substation set, aline connecting said substation set to said source of potential inseries with said inductance coil, asymmetrical conductance meansshunting said inductance coil for suppressing oscillations otherwiseproduced in said line in response to the operation of the impulsetransmitter, a pair of thermionic tubes each having an anode, a cathode,and a control electrode, means coupling the control electrodes andcathodes of said tubes to said inductance coil in push-pull relationshipwhereby one of said tubes is rendered conductive at the instant that theimpulse transmitter opens said line and the other of said tubes isrendered conductive at the instant that the impulse transmitter closessaid line, means interconnecting said tubes for rendering either one ofthe tubes non-conductive in response to the other tube becomingconductive, and an impulse repeating relay controlled by the anodecurrent of one of said tubes.

HAROLD J. MCCREARY.

REFERENCES CITED The following references are of record in the file ofthis patent:

